This invention relates to a liquid crystal display device and a method of manufacturing the liquid crystal display device, and more particularly to a method of producing two tilt domains within a liquid crystal layer and a method of fabricating a liquid crystal display device using a liquid crystal layer having the two tilt domains and a liquid crystal display device using the same.
Twisted nematic (TN) liquid crystal displays (LCDs) have been mainly used for notebook computers in spite of their narrow viewing angle characteristics. However, improving the viewing angle is a prerequisite for the replacement of cathode ray tube (CRT) displays by LCDs in monitor and TV markets. Therefore, recently, in order to enhance the viewing angle characteristics in the twisted nematic LCDs, various new concepts of LCDs have been suggested. For example, nematic liquid crystals using an in-plane switching (IPS) mode have been reported by R. Kiether, et al. (Proceedings of the 12th Int. Display Res. Conf., Society for Information Display and Institute of Television Engineers of Japan, Hiroshima, p. 547, 1992). A vertical alignment (VA) mode with a negative birefringent compensation film has also been proposed by K. Ohmuro, et al. (Digest of Technical Papers of 1997, Society for Information Display Int. Symposium, Society for Information Display, Boston, p. 845, 1997).
Although the IPS mode shows wide viewing angle characteristics comparable to the CRT display, the cell gap margin is narrower and the response time is rather slower than that of the TN mode. Furthermore, the IPS mode has a slight color shift in oblique viewing angles.
The VA mode with negative birefringent film shows a viewing angle range greater than 70xc2x0 in polar angle for all azimuthal directions and a very fast response time of less than 25 ms. However, so as to obtain the wide viewing angles, fabrication of a dual domain or a multi-domain is further necessary. A technology of fabricating the dual domain or the multi-domain within the liquid crystal layer is described by K. Ohmuro, et al. (Society for Information Display, p. 845, 1997). Here, various technologies of forming the liquid crystal having dual domain or multi-domain structure so as to obtain such wide viewing angle were proposed. They include (1) a multiple rubbing method, (2) a multiple alignment layer method, (3) an edge fringe field method, and (4) a parallel fringe field method. The multiple rubbing method, the multiple alignment layer method and parallel fringe field method have been demonstrated on the gray scale VGA level. However, these methods require cumbersome processing. For example, each panel requires more than one rubbing for one or both substrates when the multiple rubbing method is used. Each panel requires one alignment layer patterning and etching for one or both substrates when the multiple alignment layer method is used. The indium tin oxide (ITO) layer on top of the color filter layer needs to be patterned when the parallel fringe field method is used. The process of these three methods involves coating, baking, patterning, developing and stripping of the photoresist as well as one additional rubbing and photolithography process (for the multiple rubbing method), or one additional layer coating (for the multiple alignment layer method) or ITO etching on the color filter side (for the parallel fringe field method).
Therefore, the process becomes significantly more complicated and more expensive than that of the conventional single-domain process. Moreover, the multiple rubbing method involves dissymmetry in the viewing angle.
In the liquid crystal display device of in-plane switching mode (refer to xe2x80x9cAsia Display Proceedings of the 15th International Display Research Conferencexe2x80x9d Society for Information Display and the Institute of Television Engineers of Japan, Hamamatsu, Japan, p. 577, 1995) proposed so as to solve a narrow viewing angle of TN mode, liquid crystal molecules are first arranged in parallel with the substrates in the absence of the electric field and then twisted in the shape of the electric field. Therefore, it is known that the response time using the conventional IPS mode is not enough for displaying a fast moving image, in particular, in the gray scale operation. Therefore, it is important to improve the response time for high-performance LCDs.
Further, since liquid crystal molecules used in a liquid crystal display device using an in-plane switching mode has optical anisotropy, the picture shows a different color depending on the viewing direction. This is referred to as a color shift phenomenon. Such a color shift phenomenon decreases the display characteristic of the liquid crystal display device (refer to Euro display ""96, xe2x80x9cComplete suppression of color shift in in-plane switching mode LCDs with a multi-domain structure obtained by unidirectional rubbing methodxe2x80x9d).
Accordingly, one object of this invention is to simplify the technology for producing at least two tilt domains within a liquid crystal layer.
Another object of this invention is to provide a method of forming a liquid crystal display device, utilizing such simplified technology for producing at least two tilt domains within a liquid crystal layer.
A further object of this invention is to improve viewing angle characteristics in a liquid crystal display.
Another object of this invention is to shorten the response time in a liquid crystal display.
According to a broad aspect of the invention, so as to produce two domains within a liquid crystal layer, first, two electrodes are formed on a substrate, and a liquid crystal layer aligned vertically with respect to the substrate are then formed on the substrate where the substrate has two electrodes separated from each other by a selected distance. Finally, an electric field between the two electrodes is applied.
According to one aspect of the invention, a method for fabricating a liquid crystal display device, comprises the steps of: providing a first substrate; forming a first electrode and a second electrode on a surface of the first substrate; forming a homeotropic alignment layer on the first substrate having the two electrodes thereon; providing a second substrate; forming a homeotropic alignment layer on a surface of the second substrate; arranging the two substrates such that the homeotropic layers on the two substrates face each other and are separated by a selected distance; and forming a liquid crystal layer within a space between the two substrates.
According to another aspect of the invention, a method for fabricating a liquid crystal display device, comprises the steps of: providing a first substrate having an inner surface and an outer surface opposite the inner surface; forming a first electrode and a second electrode on the inner surface of the first substrate; forming a first homeotropic alignment layer on the inner surface of the first substrate having the two electrodes; providing a second substrate having an inner surface and an outer surface opposite the inner surface; forming a second homeotropic alignment layer on the inner surface of the second substrate; arranging the two substrates such that the two inner surfaces of the two substrates face each other separated by a selected distance; forming a liquid crystal layer within a space between the two substrates; and forming an optical compensating plate on at least one outer surface of the two substrates.
According to a further aspect of the invention, a liquid crystal display device comprises: a substrate having a surface; a first electrode formed on the surface of the substrate; a second electrode formed on the same surface of the substrate, an electric field being generated between the first electrode and the second electrode; a liquid crystal layer formed on the substrate surface and including liquid crystal molecules, the liquid crystal molecules being aligned vertically with respect to the substrate surface in an absence of the electric field between the electrodes.
According to still another aspect of the invention, a liquid crystal display device comprising: a substrate; a first electrode formed on a surface of the substrate; a second electrode formed on the substrate surface, an electric field being generated between the two electrodes; a liquid crystal layer formed on the substrate surface and including liquid crystal molecules, the liquid crystal molecules being aligned vertically with respect to the substrate surface in an absence of the electric field between the two electrodes; and a homeotropic alignment layer formed on at least one of upper and lower surfaces of liquid crystal layer.
According to even another aspect of the invention, a liquid crystal display device comprises: a substrate; a first electrode formed on a surface of the substrate; a second electrode formed on the substrate surface, an electric field being generated between the two electrodes; a liquid crystal layer formed on the substrate surface and including liquid crystal molecules; a homeotropic alignment layer formed on at least one of upper and lower surfaces of liquid crystal layer; and an optical compensating plate formed on at least one of upper and lower portions of the liquid crystal layer, whereby the liquid crystal molecules are aligned vertically with respect to the substrate surface in an absence of the electric field between the two electrodes.
According to yet another aspect of the invention, a liquid crystal display device comprising: a first substrate having an inner surface and an outer surface opposite the inner surface; a second substrate disposed opposite the first substrate and having an inner surface and an outer surface opposite the inner surface; a liquid crystal layer sandwiched between the inner surfaces of the two substrates and including liquid crystal molecules; a first electrode and a second electrode formed on the inner surface of the first substrate, wherein the first electrode and the second electrode are spaced apart for application of an electric field therebetween; homeotropic alignment layers respectively formed on the inner surface of the first substrate and on the inner surface of the second substrate;and an optical compensating plate disposed on at least one of the outer surfaces of the first and second substrates, wherein in the presence of the electric field between the two electrodes, the molecules are tilted from the respective electrodes towards a central region between the two electrodes.
According to even an additional aspect of the invention, a liquid crystal display device, comprises: a lower or first substrate having an inner surface and an outer surface opposite the inner surface; an upper or second substrate having an inner surface and an outer surface opposite the inner surface and disposed opposite the first substrate; a liquid crystal layer sandwiched between the two substrates and including liquid crystal molecules; a pixel electrode and a counter electrode formed on the inner surface of the first substrate, an electric field for driving the liquid crystal molecules being generated between the two electrodes; homeotropic alignment layers respectively formed on the inner surface of the lower substrate and on the inner surface of the upper substrate; a polarizer disposed outside the lower substrate; an analyzer disposed outside the upper substrate; and an optical compensating plate disposed at least one of between the liquid crystal layer and the polarizer and between the liquid crystal layer and the analyzer, whereby in an absence of the electric field between the two electrodes, the liquid crystal molecules are aligned vertically with respect to the substrate surface, and in a presence of the electric field between the two electrodes, the molecules are tilted rightward and leftward towards the center between the two electrodes.
According to still another aspect of the invention, a liquid crystal display device comprises: a lower or first substrate having an inner surface and an outer surface opposite the inner surface; an upper or second substrate having an inner surface and an outer surface opposite the inner surface and disposed opposite the first substrate; a plurality of gate bus lines and a plurality of data bus lines intersecting the plurality of gate bus lines, arranged in a matrix configuration on a surface of the first substrate and defining a plurality of pixel regions each bounded by a pair of the plurality of gate bus lines and a pair of the plurality of data bus lines; a liquid crystal layer sandwiched between the inner surfaces of the two substrates and including liquid crystal molecules; a pixel electrode and a counter electrode formed on the inner surface of the first substrate, an electric field for driving the liquid crystal molecules being generated between the two electrodes; a plurality of switching devices corresponding respectively to the plurality of pixel regions, each of the plurality of switching devices being connected to a corresponding one of the plurality of data bus lines and a corresponding one of the plurality of pixel electrodes; homeotropic alignment layers respectively formed on the inner surface of the second substrate and on the inner surface of the first substrate; a polarizer disposed outside the first substrate; an analyzer disposed outside the second substrate; and an optical compensating plate interposed at least one of between the liquid crystal layer and the polarizer and between the liquid crystal layer and the analyzer, whereby in a presence of the electric field between the pixel electrode and the counter electrode, the molecules are tilted rightward and leftward towards the center between the two electrodes.